The University of Minnesota has been under contract to the National Cancer Institute in evaluating the health of workers certified by the American Registry of Radiologic Technologists (ARRT) since February 1982. A 16-page optical scan questionnaire was sent to participants to obtain information on cancer history, risk factors, work history, and personal medical x-ray exposures. Over 90,000 of the 145,000 technologists under study responded to the full-length questionnaire. An additional 14,000 technologists provided information on their history of cancer, myocardial infarction, and thyroid conditions during an abbreviated telephone interview. Reported leukemias and cancers of the breast, thyroid, and lung were validated by obtaining hospital, pathology, and other reports. Computer linkage with the records of the nation's largest commercial dosimetry company has provided at least partial exposure histories on over 85,000 technologists. Additionally, specific exposure information was obtained from employers for persons who developed leukemia, or cancer of the breast, thyroid, or lung as well as for a random sample of the entire cohort. This second survey is being undertaken to obtain detailed information on cancer incidence during the years since the first questionnaire. Occupational and personal exposures to diagnostic x-rays are already coded and crude estimates of whole-body radiation doses can be made. A second follow-up will enable us to link the occurrence of subsequent cancer with these previous measures of radiation exposure. Incident cancers of the breast and thyroid are of particular interest because mortality data are incomplete.